TMax DX - Screeching/squeal on WOT throttle sometimes

[8500rpm]

Hello all once again (been gone for awhile).

Had this phenomenon for awhile, but have not really done anything (yet).

I had the belt replaced under Warranty bulletin on my Tmax DX-18 awhile ago (i.e recall from Yamaha, dunno why).

After the replacement byt Yamaha shop, sometimes (not often) on wide open throttle acceleration (not stand still) but maybe doing 30-40km/h and full gas the bike 'hesitates' for a microsecond and you can hear a loud screeching squealing sound.

It sounds like a bearing is about to blow, OR as if the belt would be slipping (also feels like that). I had the scooter to the ship again, but of course when they test road it they couldn't notice it (it only happens to me like once a week or so).

Is this a known problem, belt to lose, to tight, something slipping or something else?


Very happy for any wise input


Markus

[MrGrumpy]

Hmmm Presumably you mean you had the final drive belt changed as part of the recall?

I'm not the greatest mechanical expert (an understatement), but if you are getting funny noises on acceleration, then this is likely to be something to do with the CVT and V-belt rather than the final drive belt.

There have been troubles with the mk6 CVT drive - I had a new CVT eventually as did someone else on here (forget the name). However, the symptoms I had weren't quite the same - I had a delay between the throttle being opened and drive coming in, but this was at quite high speeds, not at low speeds. I did hear a nasty mechanical squeal though, though this again was at high revs & speeds, when I got beyond 5500 rpm at speed.

There again, I did get squealing noises at lower speeds from the final drive belt on my mk4 - possibly down to a worn bearing in the front pinion of the belt. However, the mk4 and mk6 have completely different designs in this area.

So its difficult to be sure, but since there have been troubles with the CVT on some mk6s,I do suspect this is the root of your trouble. Some people got a replacement automatically as part of the recall, I had to pursue mine via Yamaha, though I've read on here now that Yamaha will replace the CVT 'on demand' . Hope this helps.

[8500rpm]

Thanks Mr Grumpy!

It never happens from 0mph start, but say I'm following cars at say 20-30mph, then get ready to overtake, WOT...hiccup in acceleration for a micro-second, screeching sound and off I go again... it's very hard to re-produce.

I will discuss the above with my shop. Will update you here on MaxiMuppets with findings.

Markus

[MrGrumpy]

Thanks Mr Grumpy!

It never happens from 0mph start, but say I'm following cars at say 20-30mph, then get ready to overtake, WOT...hiccup in acceleration for a micro-second, screeching sound and off I go again... it's very hard to re-produce.

It does sound a bit like mine, but at much lower speeds. Curious!

[Chocky]

I had the same problem on my Mk4. It turned out to be the final drive belt moving across the pulley slightly on acceleration and rubbing against the offside flange on the rear wheel toothed pulley. This led to the wearing away of the rubber on that side of the belt, exposing a steel belt edge which was sandwiched in the middle of the rubber belt. It was this steel belt edge which caused the screech by rubbing against the offside flange. After checking that the rear wheel was correctly aligned, I had the belt changed which solved it. I wondered afterwards whether turning the belt around was possible, as that would have worked as well.

As to the Mk6 belt - I cannot comment as I don't have any experience of it.

[MrGrumpy]

As I said, I did have a sort of whining noise from the final drive belt on my mk4, at around 30mph. But the Final drive belt on the mk6 is very different to that on the mk4 - half the width for one thing! And the belt on 8500rpm's bike has already been changed under the recall. However it might be worth checking out.

[EvilRacer329]

That does sound an awful lot like the Mk6 belt slipping issue. I advised my dealer to give Yamaha technical a call and, what do you know, they immediately authorised the entire CVT be replaced. The technical service bulletin number in question is TSI2019/02 and was incorporated into production bikes from September 2018 onwards. If your bike was made after this, then it's not likely to be the same issue I'd wager.

It's weird that it would happen at low speeds, but the cause - dust accumulating on the surface of the CVT belt - could cause slippage anytime there is sufficient torque being applied.

Let us know how you get on!

Nick